The conversion of fatty acids to linear alkanes by deoxygenation using catalysts including nickel and molybdenum is already known. A process for the conversion of linear alkanes to branched alkanes by isomerisation using specified metallosilicates, especially a ferrierite catalyst containing platinum has been described in EP-A-0653399. EP-A-1396531 describes a two-step process for the production of a hydrocarbon from a fatty acid or a fatty acid ester, involving deoxygenation in a first step and isomerisation in a second step. WO 2006/100584 describes a process for the production of diesel fuel from vegetable and animal oils. It is an object of the invention to provide an improved process for the conversion of oxygenated organic materials, especially fatty acids, to hydrocarbon mixtures containing a high level of non-linear components in a single-step process.